Can ultrasound reveal abnormalities associated with poor survival in cloned calves before birth?

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The study began with a possible explanation for the high pregnancy loss and prenatal illness and death encountered in cloned animals: insufficient placental nutrition or steroid production might indirectly compromise fetal survival, as proposed in Hashizume et al. (2002, Cloning and Stem Cells 4(3), 197–209). The researchers hypothesized that ultrasound characterization of the placenta in bovine clones could help predict abnormalities in fetal development and well-being during pregnancy.

In a longitudinal comparative study, they examined surrogate heifers carrying cloned fetuses (n = 37) and fetuses produced by traditional embryo transfer (n = 5), at three stages of gestation: Days 70, 100 and 200. Direct ultrasound observations recorded the thickness and shape of the amniotic membrane, utero-placental thickness, the shape and length of placentomes in the fetal area, and the shape and appearance of the umbilical cord. Analysis used a repeated measures linear model, with day as the repeated factor.

Of the cloned pregnancies, 30 females were still pregnant at Day 70, and only 16 reached Day 100. Of those reaching Day 100, 63% had varying degrees of amniotic membrane and/or umbilical cord abnormalities. No placental abnormalities or abortions were observed in the control group. At Day 100, the amniotic membrane abnormalities included irregularities and rosary-like nodules visible in cross-section. Highly echo-bright spikes or irregularities around the umbilical cord were seen at Day 100 in 38% of the clones (n = 6); all of these also had amniotic membrane abnormalities.

Among cloned pregnancies with amniotic membrane and/or umbilical cord problems, 30% aborted between Days 100 and 200. Among affected pregnancies that reached term, at Days 264–278 (n = 7), all calves but one died at birth or during the first month of life.

Across all three gestational stages, placentomes in cloned embryos were larger than in control embryos (P = 0.003; least-squares mean [LSM]: clones, 4.34 cm; controls, 2.97 cm). Over the same period, the clones' amniotic membranes became thicker compared with controls (P = 0.0001; LSM: clones, 0.25 cm; controls, 0.11 cm). Utero-placental thickness also varied. At Day 70, this layer was thicker in clones than in controls (LSM: clones, 0.32 cm; controls, 0.30 cm), but at Day 200 it was thinner than in controls (LSM: clones, 0.38 cm; controls, 0.40 cm).

The researchers concluded that morphological abnormalities of the placentomes, amniotic membrane and umbilical cord arise during gestation in cloned bovine fetuses and could potentially compromise normal fetal development. They also concluded that ultrasound monitoring of cloned-animal pregnancies is useful for characterizing changes in fetal membranes.

The work was funded by a Strategic Project Grant from the Natural Sciences and Engineering Research Council (NSERC) Canada.